Ionic liquids are essentially salts in a liquid state, and are described in U.S. Pat. No. 4,764,440, U.S. Pat. No. 5,104,840, and U.S. Pat. No. 5,824,832. The properties vary extensively for different ionic liquids, and the use of ionic liquids depends on the properties of a given ionic liquid. Depending on the organic cation of the ionic liquid and the anion as well as temperatures, the ionic liquid can have very different properties.
Acidic ionic liquid may be used as a catalyst in various chemical reactions, such as the alkylation of iso-butane with olefins. The reaction of iso-butane with olefins to produce an alkylate product is a highly exothermic reaction. One way to control the temperature of the reactor and system is by vaporizing a portion of the light hydrocarbons. However, controlling the temperature by vaporization is undesirable because it makes the reactor operation, the ionic liquid dispersion, and the acid concentration more difficult to control. Therefore, it is believed to be more desirable to control the temperature while the reactants and products are maintained in liquid phase.
Indeed, maintaining the reactants and products in liquid phase allows for heat exchange with cooling or process fluid to be utilized to remove heat from the liquid mixture of reactants and products. While passing a liquid stream with a mixture of reactants and products from a reactor to a heat exchanger may be an effective and efficient design, there are benefits associated with combining the reactor and heat exchanger into a single unit. For example, the combination of the reactor and heat exchanger into one unit can reduce piping, plot space and costs.
However, current designs for such combined units are not properly configured to be effectively and efficiently utilized for use with ionic liquid catalyst processes. For example, one current designs of such a combined reactor and heat exchanger utilizes pump impellers for fluid mixing, dispersion and circulation. The process fluid is on the shell side of the heat exchanger with limited fluid velocities, and thus the heat transfer would be poor for a fluid containing viscous liquid acid catalyst. In addition, a wide distribution of dispersed-phase liquid droplets and emulsion fluid are created by the high shear pump impellers, which makes downstream separation of the dispersed liquid droplets of ionic liquid catalyst difficult.
Therefore, there remains a need for a design of a combined reactor and heat exchanger that can be used in association with ionic liquid catalyst.